Water pump and assembly method for water pump

ABSTRACT

Water pump has a drive shaft inside pump housing, a pulley provided at one end of drive shaft, and impeller fitted onto other end portion of drive shaft through fitting hole. Restraining part restraining maximum fitting position of impeller in axial direction is provided between other end portion of drive shaft and fitting hole of the impeller, fixing member restraining axial direction movement of impeller positioned in the maximum fitting position in cooperation with restraining part is provided at tip end side of other end portion of the drive shaft, and the cross-sectional shape of fitting part, which is fitted into fitting hole of the impeller, of other end portion of drive shaft is formed as a rotation restraining part, and cross-sectional shape of fitting hole of impeller is formed into same cross-sectional shape as fitting part of other end portion of drive shaft, as rotation restraining part.

TECHNICAL FIELD

The present invention relates to a water pump applied to, for instance, an engine cooling device of a vehicle and circulating cooling water in the cooling device, and relates to an assembly method for the water pump.

BACKGROUND ART

As this kind of water pump in related arts, a water pump disclosed in the following Patent Document 1 has been known.

When briefly explaining the water pump, the water pump has a pump housing having therein a pump chamber, a drive shaft formed into a cylindrical column with synthetic resin material and rotatably supported in the pump chamber, a synthetic resin-made pulley integrally connected to one end portion of the drive shaft through a flange wall and rotating by power transmitted from an external unit, a ball bearing provided on an inner circumferential side of the pulley through a cylindrical metal-made insert, a synthetic resin-made impeller provided at the other end portion of the drive shaft, and a mechanical seal interposed between the pump housing and the drive shaft and sealing a gap between the pump chamber and the ball bearing.

The impeller and the drive shaft are bonded so as to be able to rotate integrally with each other by vibration-welding an inner circumferential surface of an insertion hole having an almost circular shape in cross section which is formed by penetrating a middle of the impeller to an outer peripheral surface of the other end portion of the drive shaft which is inserted into the insertion hole of the impeller.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No. JP2002-349481

SUMMARY OF THE INVENTION

However, although the impeller and the drive shaft are bonded so as to allow the integral rotation by the vibration welding as described above, in a case where this vibration welding is insufficient, bonding strength between welding surfaces is reduced, and the bonded welding surfaces come off each other upon pressurizing and sending cooling water, then there is a risk that the drive shaft will idle or race with respect to the impeller or the impeller will come off or fall off the drive shaft.

The present invention was made in view of the above technical problem of the related art water pump. An object of the present invention is therefore to provide a water pump that is capable of preventing the drive shaft from idling or racing with respect to the impeller and preventing the impeller from coming off the drive shaft.

In the present invention, a water pump comprises: a drive shaft inserted and located in an inside of a pump housing and formed with synthetic resin material; a pulley provided at one end portion of the drive shaft and rotating integrally with the drive shaft, the pulley being configured to rotate by transmission of power from a drive source; and an impeller formed with synthetic resin material, having a fitting hole and fitted onto the other end portion of the drive shaft through the fitting hole. And, the drive shaft and the impeller are configured so that a restraining part that restrains a maximum fitting position of the impeller in an axial direction is provided between the other end portion of the drive shaft and the fitting hole of the impeller, a fixing member that restrains an axial direction movement of the impeller positioned in the maximum fitting position in cooperation with the restraining part is provided at a tip end side of the other end portion of the drive shaft, and a cross-sectional shape of a fitting part, which is fitted into the fitting hole of the impeller, of the other end portion of the drive shaft is formed as a rotation restraining part, and a cross-sectional shape of the fitting hole of the impeller is formed into the same cross-sectional shape as the fitting part of the other end portion of the drive shaft, as the rotation restraining part.

According to the present invention, a connecting force of the impeller and the drive shaft is increased, thereby preventing the drive shaft from idling or racing with respect to the impeller and preventing the impeller from coming off the drive shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross section of a water pump according to a first embodiment of the present invention.

FIG. 2 is a perspective exploded view of the water pump according to the first embodiment.

FIG. 3 is a drawing viewed from an arrow A of FIG. 1.

FIG. 4A is an enlarged perspective view of a drive shaft of the first embodiment. FIG. 4B is a sectional view taken along a line A-A of FIG. 4A.

FIG. 5A is a perspective view of essential parts of the first embodiment. FIG. 5B is an enlarged view of FIG. 5A.

FIG. 6 is a perspective view of aback surface of an impeller of the first embodiment.

FIG. 7 is a perspective exploded view showing an assembly process in which the impeller is connected to the drive shaft.

FIG. 8 is a perspective view showing an assembly state of the impeller and the drive shaft with the impeller partly cut.

FIG. 9A is an enlarged perspective view of a drive shaft of a second embodiment of the present invention. FIG. 9B is a sectional view taken along a line B-B of FIG. 9A.

FIG. 10A is an enlarged perspective view of a drive shaft of a third embodiment of the present invention. FIG. 10B is a sectional view taken along a line C-C of FIG. 10A.

FIG. 11A is an enlarged perspective view of a drive shaft of a fourth embodiment of the present invention. FIG. 11B is a sectional view taken along a line D-D of FIG. 11A.

FIG. 12A is an enlarged perspective view of a drive shaft of a fifth embodiment of the present invention. FIG. 12B is a sectional view taken along a line E-E of FIG. 12A.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of a water pump according to the present invention will be explained below with reference to the drawings. This water pump 1 is applied to a cooling device to circulate antifreeze (ethylene glycol), which is cooling water, between a radiator and an internal combustion engine of a vehicle.

As shown in FIGS. 1 and 2, the water pump 1 is formed mainly by a pump housing 2 directly secured to a side portion of a cylinder block (not shown) of an internal combustion engine (not shown) with bolts and having a pump chamber 3 at a front end portion, on a cylinder block side, of the pump housing 2, a pulley 5 rotatably supported by a single-unit ball bearing 4, which is a bearing unit, on a rear end side of the pump housing 2, a metal-made insert 6 interposed between the pulley 5 and the ball bearing 4, a drive shaft 7 which is inserted and located in an inside of the pump housing 2 and whose one end side is formed integrally with the pulley 5, an impeller 8 secured to the other end side of the drive shaft 7 and rotatably accommodated in the pump chamber 3, and a mechanical seal 9 interposed between the pump housing 2 and the drive shaft 7 and sealing a gap between the pump chamber 3 and the ball bearing 4.

The pump housing 2 is formed as a single unit with aluminium alloy material. A housing body 10, on a pump chamber 3 side, of the pump housing 2 has an irregular annular shape. The pump housing 2 has a stepped cylindrical portion 11 on a rear end side of the housing body 10.

The housing body 10 has, at a front end thereof, a ring-shaped flat mounting surface 10 a that contacts a flat surface area of a side portion of the cylinder block. The housing body 10 also has, at an outer periphery thereof, a plurality boss portions 10 c each having a bolt hole 10 b into which a fixing bolt screwed into and fixed to the cylinder block is inserted.

Further, the housing body 10 has, in an inside thereof, an outlet port 10 d that discharges the cooling water, which flows into the pump chamber 3 from an inlet port, on a radiator (not shown) side, of the housing body 10 (the pump housing 2), to an inside of a water jacket in the cylinder block by and according to rotation of the impeller 8.

The cylindrical portion 11 is formed, as shown in FIGS. 1 to 3, from a large diameter cylindrical portion 11 a on a pump chamber 3 side, a middle diameter cylindrical portion 11 b extending from the large diameter cylindrical portion 11 a toward the ball bearing 4 and a small diameter cylindrical portion 11 c extending from the middle diameter cylindrical portion 11 b to one end side of the drive shaft 7.

The middle diameter cylindrical portion 11 b is provided, on a lower side in a gravity direction, with a drain hole 12 penetrating the middle diameter cylindrical portion 11 b in an up-and-down direction in order for drop of the cooling water leaking from the mechanical seal 9 to fall into the drain hole 12. The middle diameter cylindrical portion 11 b is also provided, on a lower side of the drain hole 12, with a drain chamber 13 extending to an inside of the large diameter cylindrical portion 11 a and collecting and storing the drop of the cooling water from the drain hole 12. A lower end opening of this drain chamber 13 is liquid-tightly sealed by a drain cap 14.

The ball bearing 4 is a common bearing. As shown in FIGS. 1 and 2, the ball bearing 4 has an inner ring 4 a press-fitted into the small diameter cylindrical portion 11 c, an outer ring 4 b press-fitted into the insert 6 and a plurality of balls 4 c rollably provided between the inner ring 4 a and the outer ring 4 b through a holder.

A maximum press-fit position of the inner ring 4 a in its axial direction is restricted by a rear end surface of the middle diameter cylindrical portion 11 b of the cylindrical portion 11. On the other hand, an axial direction position of the outer ring 4 b is previously set by a press-fit length into the insert 6.

As shown in FIGS. 1 and 2, the ball bearing 4 is provided, at front and rear ends thereof in the axial direction, a pair of first and second seal members 15 and 16 to prevent entry of dust into an inside of the ball bearing 4. Both of the seal members 15 and 16 have a substantially ring-shape, and are oppositely disposed so as to cover the axial direction both sides of the ball bearing 4.

The first seal member 15 is fixed with the first seal member 15 sandwiched between the middle diameter cylindrical portion 11 b and one end surface of the inner ring 4 a. The second seal member 16 is fixed by a retainer 17 that is a retaining member with the second seal member 16 sandwiched between the retainer 17 and the other end surface of the inner ring 4 a.

As shown in FIGS. 1 and 2, the pulley 5 is molded integrally with the drive shaft 7 with synthetic resin material containing an after-mentioned glass fiber 26. The pulley 5 has a flange wall 5 a that is a disk-shaped end wall extending from the one end side of the drive shaft 7 in a radial direction, a large diameter cylindrical base portion 5 b bending from an outer peripheral edge of the flange wall 5 a in an axial direction of the drive shaft 7 and a belt attaching portion 5 c provided on an outer circumferential surface of the cylindrical base portion 5 b.

As shown in FIGS. 1 and 2, the flange wall 5 a is provided, at substantially regular intervals in a circumferential direction thereof, with six penetration holes 18 penetrating the flange wall 5 a in the axial direction for insertion of a jig upon assembly. The flange wall 5 a is also provided, on an outer surface thereof, with a stiffening rib 19 formed integrally with the flange wall 5 a along the radial direction from the middle of the outer surface of the flange wall 5 a.

As shown in FIG. 1, the cylindrical base portion 5 b is provided, on an inner circumferential side thereof, with the above mentioned metal-made cylindrical insert 6. This insert 6 has a cylindrical body 6 a and a flange portion 6 b formed integrally with a top end of the body 6 a. The insert 6 is fixedly connected to the pulley 5 with the flange portion 6 b embedded in the cylindrical base portion 5 b upon resin-molding of the pulley 5.

The belt attaching portion 5 c is configured so that a rotation force is transmitted to a wave-toothed outer periphery of the belt attaching portion 5 c via a transmission belt that is wound around a drive pulley (not shown) fixed to a top end portion of a crankshaft (not shown).

As shown in FIG. 1, the drive shaft 7 is formed into a cylindrical column having a stepped shape with synthetic resin material containing the after-mentioned glass fiber 26. The drive shaft 7 has a large diameter shaft portion 7 a, as one end portion of the drive shaft 7, which is molded integrally with a middle of the flange wall 5 a of the pulley 5 along the axial direction, a middle diameter shaft portion 7 b, as the other end portion of the drive shaft 7, which extends from the other end of the large diameter shaft portion 7 a in the axial direction, and a small diameter shaft portion 7 c, also as the other end portion of the drive shaft 7, which extends from the other end of the middle diameter shaft portion 7 b in the axial direction.

Further, the drive shaft 7 is shaped into a tapered shape whose diameter becomes smaller gradually or step by step from the large diameter shaft portion 7 a toward a tip end of the small diameter shaft portion 7 c. That is, the drive shaft 7 is formed to take account of draft when being pulled out of a mold after injection molding while ensuring rigidity of the large diameter shaft portion 7 a that is a connecting portion with the pulley 5.

The middle diameter shaft portion 7 b is configured so that, as shown in FIGS. 1 and 8, the impeller 8 is fitted onto the middle diameter shaft portion 7 b so as to range from the middle diameter shaft portion 7 b to the small diameter shaft portion 7 c through an after-mentioned fitting hole 23. A part (a fitting part 20) of the middle diameter shaft portion 7 b, which is a fitting range or a fitting area into the fitting hole 23, is formed into a non-perfect circle in cross section, as a rotation restraining part that restrains a relative rotation of the impeller 8 with respect to the drive shaft 7.

More specifically, as shown in FIGS. 4A and 4B, the fitting part 20 from a substantially axial direction middle position of the middle diameter shaft portion 7 b up to an end edge, on a small diameter shaft portion 7 c side, of the middle diameter shaft portion 7 b is provided, in 180° positions in a circumferential direction on an outer peripheral surface of the fitting part 20, with a pair of recessed portions 21 and 21. Each of these recessed portions 21 and 21 has a curved outer peripheral surface, and both circumferential direction edges of each recessed portion 21 continue to an outer peripheral surface of the middle diameter shaft portion 7 b by a gentle or smooth curved surface.

With the above-described structure, the fitting part 20 of the middle diameter shaft portion 7 b, which is the fitting area into the fitting hole 23, has a non-perfect circle cocoon shape whose cross section is symmetrical about a shaft center and which has a smooth recessed and bulging shape.

The small diameter shaft portion 7 c serves as a guide portion when assembling the impeller 8. The small diameter shaft portion 7 c is formed so that the tip end portion of the small diameter shaft portion 7 c protrudes from a front end side of the impeller 8. This protruding portion 7 d has, at tip edge thereof, a tapered surface 7 e.

A ring-shaped first stepped portion 22 that forms a part of a restraining part is provided at a connecting portion between the middle diameter shaft portion 7 b and the small diameter shaft portion 7 c so as to be orthogonal to the axial direction.

The impeller 8 is formed as a single unit with synthetic resin material. As shown in FIGS. 1 to 3 and 6, the impeller 8 has a substantially disk-shaped base portion 8 a, a shaft portion 8 b protruding in front and rear directions from a middle of the base portion 8 a and eight vane portions 8 c formed radially from an outer circumferential surface of the shaft portion 8 b on a front surface side of the base portion 8 a.

The base portion 8 a has a predetermined thickness. The base portion 8 a rotates with a clearance given between a back surface of the pump chamber 3 and the base portion 8 a. As shown in FIGS. 2, 3 and 6, the base portion 8 a is provided, in 180° positions in a circumferential direction also substantially radially middle positions on a back surface thereof, with a pair of small diameter penetration holes 8 d. The cooling water flows to the back surface of the base portion 8 a through the small diameter penetration holes 8 d, thereby cooling the mechanical seal 9 and suppressing burn due to slide friction between the mechanical seal 9 and the drive shaft 7.

The shaft portion 8 b has the fitting hole 23 which penetrates the shaft portion 8 b in the axial direction and into which the other end portion of the drive shaft 7 is inserted and fitted. The fitting hole 23 has, in a position corresponding to the fitting part 20 of the middle diameter shaft portion 7 b when being fitted onto the drive shaft 7, a large diameter fitting hole portion 23 a, as the rotation restraining part, having a substantially same cross-sectional shape as the cross-sectional shape of the fitting part 20.

That is, the fitting part 20 of the middle diameter shaft portion 7 b is formed into the cocoon shape in cross section, and a shape of an inner circumferential surface of the large diameter fitting hole portion 23 a has the same cross-sectional shape as the cocoon shape of the middle diameter shaft portion 7 b, then the impeller 8 is fitted onto the drive shaft 7 so as to range from the middle diameter shaft portion 7 b to the small diameter shaft portion 7 c. Further, the fitting hole 23 has, in a position where the small diameter shaft portion 7 c is inserted, a small diameter fitting hole portion 23 b having a cylindrical shape corresponding to a shape of an outer peripheral surface of the small diameter shaft portion 7 c.

The large diameter fitting hole portion 23 a is formed so that a diameter of the large diameter fitting hole portion 23 a is slightly larger than a maximum diameter of the fitting part 20 gradually tapering toward the tip end side of the drive shaft 7, and has a uniform bore. The small diameter fitting hole portion 23 b is formed so that a diameter of the small diameter fitting hole portion 23 b is slightly larger than a maximum diameter of the small diameter shaft portion 7 c, and has a uniform bore. Then, the impeller 8 and the drive shaft 7 are fitted together by clearance fit.

Further, a ring-shaped second stepped portion 24 that forms a part of the restraining part is provided between the large diameter fitting hole portion 23 a and the small diameter fitting hole portion 23 b of the fitting hole 23 of the impeller 8.

This second stepped portion 24 is formed so as to be orthogonal to the axial direction. Then, when fitting the impeller 8 onto the drive shaft 7, the second stepped portion 24 contacts the first stepped portion 22 also formed on the drive shaft 7 side so as to be orthogonal to the axial direction, then a further axial direction movement of the impeller 8 to the drive shaft 7 side is restrained.

Therefore, a maximum fitting position of the impeller 8 with respect to the drive shaft 7 is fixed by these first and second stepped portions 22 and 24, and the further axial direction movement of the impeller 8 from here to the drive shaft 7 side is restrained.

In addition, as mentioned above, when connecting the impeller 8 to the drive shaft 7, the small diameter shaft portion 7 c protrudes from the front end side of the impeller 8, and a metal-made push-nut 25 that is a fixing member is fitted onto and engaged with or fixed to this protruding portion 7 d.

As shown in FIGS. 1 and 2, the push-nut 25 is formed into a thin disk shape, and has, in the center thereof, an insertion hole 25 a whose diameter is smaller than the small diameter shaft portion 7 c of the drive shaft 7.

The push-nut 25 also has a plurality of nail portions 25 c formed through a plurality of cutting portions 25 b that are cut from an outer circumference of the push-nut 25 toward the insertion hole 25 a. The push-nut 25 is fixed to the protruding portion 7 d by bite of a tip edge of each nail portion 25 c into an outer peripheral surface of the protruding portion 7 d in a line-contact or point-contact state at a maximum pushing position of the push-nut 25. With this fixing, an axial direction movement of the impeller 8 toward an opposite side to the first and second stepped portions 22 and 24 is restrained.

The mechanical seal 9 is a common seal. As shown in FIGS. 1 and 2, the mechanical seal 9 has a cartridge portion 9 a fixed to an inner circumferential surface of the small diameter cylindrical portion 11 c of the cylindrical portion 11, a sleeve portion 9 b fixed to the outer peripheral surface of the middle diameter shaft portion 7 b of the drive shaft 7 and a seal portion 9 c provided and sliding between an inner circumferential side of the cartridge portion 9 a and an outer circumferential side of the sleeve portion 9 b.

Here, as mentioned above, the pulley 5 and the drive shaft 7 are integrally molded by the mold with the synthetic resin, and when molding these pulley 5 and drive shaft 7, synthetic resin material in which short glass fiber 26 is mixed is used.

This synthetic resin material is poured or injected into the mold from a position corresponding to a tip end surface of the small diameter shaft portion 7 c of the drive shaft 7. Then, when the synthetic resin material flows up to the connecting position of the large diameter shaft portion 7 a with the flange wall 5 a along the axial direction, the synthetic resin material radially flows in a radial direction toward an outer peripheral edge position of the belt attaching portion 5 c of the pulley 5, and thus the mold is filled with the synthetic resin material.

Upon molding, the glass fiber 26 existing close to sections where the synthetic resin material contacts the mold, i.e. the glass fiber 26 existing close to the pulley 5 and the outer peripheral surface of the drive shaft 7, is oriented in a flow direction of the synthetic resin material. For instance, as shown in FIGS. 5A and 5B, a glass fiber 26 a existing inside the middle diameter shaft portion 7 b of the drive shaft 7 is oriented along a circumferential direction, whereas a glass fiber 26 b existing close to the outer peripheral surface of the middle diameter shaft portion 7 b (or of the drive shaft 7) is oriented along the axial direction (see arrows in FIG. 5B).

[Assembly Method of Impeller and Drive Shaft]

An assembly method in which the impeller 8 is connected or fixed to the drive shaft 7 will be explained below.

First, by relatively rotating the impeller 8 with respect to the drive shaft 7, positioning of the fitting part 20 of the drive shaft 7 and the large diameter fitting hole portion 23 a of the impeller 8 is previously made.

Next, as shown in FIG. 7, the impeller 8 is moved to the large diameter shaft portion 7 a side along the axial direction from a tip end edge of the small diameter shaft portion 7 c of the drive shaft 7 while being fitted onto the drive shaft 7, and pushed up to a position (the maximum fitting position) where the second stepped portion 24 of the impeller 8 contacts the first stepped portion 22 of the drive shaft 7. At this time, by further pushing the impeller 8 toward the large diameter shaft portion 7 a while rotating the impeller 8 with respect to the drive shaft 7, a check whether fitting of the large diameter fitting hole portion 23 a to the fitting part 20 is secured is carried out.

Subsequently, while holding the impeller 8 at the maximum fitting position, the push-nut 25 is fitted onto the protruding portion 7 d of the small diameter shaft portion 7 c which protrudes from the front end side of the shaft portion 8 b of the impeller 8 while elastically deforming each nail portion 25 c in a diameter-widening direction, then pushed up to a front end surface position of the shaft portion 8 b on the protruding portion 7 d.

With this, the push-nut 25 is fitted onto and engaged with the outer peripheral surface of the protruding portion 7 d with each nail portion 25 c remaining elastically deformed in the diameter-widening direction. Then, the tip edge of each nail portion 25 c bites the outer peripheral surface of the protruding portion 7 d by an elastic force (a restoring force) of the nail portion 25 c in a diameter-reducing direction, thereby fixing an axial direction position of the push-nut 25.

By the above manner, as shown in FIG. 8, the relative rotation of the impeller 8 is restrained by the fitting part 20 formed into the substantially cocoon shape in cross section, of the middle diameter shaft portion 7 b of the drive shaft 7 and the large diameter fitting hole portion 23 a having the same cocoon shape as the fitting part 20, of the impeller 8. In addition, the axial direction movement of the impeller 8 is restrained by the restraining part formed from the first and second stepped portions 22 and 24 also by the push-nut 25. The impeller 8 is then firmly secured to the drive shaft 7 with the relative rotation and the axial direction movement of the impeller 8 restrained.

[Working and Effect of First Embodiment]

Hence, according to the present embodiment, when the crankshaft of the engine rotates and the pulley 5 is driven and rotates, the impeller 8 rotates and performs a pumping operation through the drive shaft 7 molded integrally with the pulley 5, and the cooling water is pressurized and sent from the outlet port 10 d to the water jacket of the engine, then the whole internal combustion engine is cooled.

At this time, a moment force (force in the circumferential direction) by or associated with transmission of a rotation force and an axial load (force in the axial direction) toward the tip end of the drive shaft 7 due to a reaction force when pressurizing and sending the cooling water by each of the vane portions 8 c act on the connecting portion between the drive shaft 7 and the impeller 8. If a connecting strength between the drive shaft 7 and the impeller 8 is low, there is a risk that the drive shaft 7 will idle or race with respect to the impeller 8 due to insufficient transmission of the rotation force between the drive shaft 7 and the impeller 8, or the impeller 8 will come off or fall off the drive shaft 7 caused by the fact that the connecting portion between the drive shaft 7 and the impeller 8 cannot withstand the axial load.

For this problem, in the present embodiment, by the fitting part 20 of the middle diameter shaft portion 7 b and the large diameter fitting hole portion 23 a of the impeller 8, which have the substantially same cocoon shape in cross section, the relative rotation of the impeller 8 with respect to the drive shaft 7 is restrained, then the connecting strength against force in the rotation direction, i.e. a rotation suppressing force, is improved.

That is, when the drive shaft 7 rotates by the rotation of the pulley 5, by the fact that the fitting part 20 and the large diameter fitting hole portion 23 a bite or are engaged with each other, the relative rotation of the impeller 8 is restrained, then the rotation force is surely transmitted to the impeller 8.

Further, in the present embodiment, since the axial direction movement of the impeller 8 is surely restrained in cooperation with the first and second stepped portions 22 and 24 and the push-nut 25, the connecting strength is further improved.

That is, even if the axial load toward the tip end of the drive shaft 7 along the axial direction acts on the impeller 8, since the tip edge of each nail portion 25 c provided on an inner circumferential side of the push-nut 25 bites the outer peripheral surface of the small diameter shaft portion 7 c by the elastic force and is firmly engaged with or fixed to the outer peripheral surface of the small diameter shaft portion 7 c, the movement of the impeller 8 is firmly restrained.

Therefore, according to the present embodiment, the connecting strength between the drive shaft 7 and the impeller 8 is improved, it is thus possible to surely suppress the idle or racing of the drive shaft 7 with respect to the impeller 8 and the come-off of the impeller 8 from the drive shaft 7.

Further, in the present embodiment, the push-nut 25 is made of metal, whereas the drive shaft 7 is formed with synthetic resin material. For this reason, there is a need to consider that due to the fact that a contact point of the small diameter shaft portion 7 c with the tip edge of each nail portion 25 c of the push-nut 25 is eroded by resin creep (aged deterioration), there is a possibility that the push-nut 25 will come off the drive shaft 7 and the drive shaft 7 and the impeller 8 will be disconnected.

Thus, in the present embodiment, by using, as the push-nut 25, a nut formed into the thin disk shape and fixed to the small diameter shaft portion 7 c by the line-contact or the point-contact, a contact range or a contact area between the push-nut 25 and the small diameter shaft portion 7 c can be extremely small. That is, even if the resin creep occurs in the contact point of the small diameter shaft portion 7 c with the push-nut 25 then the push-nut 25 moves to the tip end side of the drive shaft 7, since an area where the resin creep occurs is quite narrow, ill effect due to the resin creep is reduced, and the connection or fixing of the drive shaft 7 and the impeller 8 can be maintained.

In addition, the small diameter shaft portion 7 c of the drive shaft 7 is formed so as to protrude from the front end side of the impeller 8, and the push-nut 25 is fitted onto and engaged with the protruding portion 7 d in a position of the front end surface of the shaft portion 8 b of the impeller 8. As a consequence, even if the resin creep occurs and the push-nut 25 moves to the tip end side of the drive shaft 7, the nail portion 25 c of the push-nut 25 bites and is fixed to a position after movement of the push-nut 25 on the drive shaft 7, then the connection or fixing of the drive shaft 7 and the impeller 8 is maintained.

Furthermore, in the present embodiment, since the fitting part 20 is formed into the cocoon shape that is the smooth recessed and bulging shape having no corner or no edge, a stress concentration is hard to occur as compared with a shape having the corner or the edge.

Moreover, since the cross section of the fitting part 20 is symmetrical about the shaft center, the stress concentration is hard to occur irrespective of a rotation direction. For instance, even in a case where a rotation force in a reverse rotation direction, which is opposite to a normal rotation direction, acts on the drive shaft 7 or the impeller 8 by the cooling water flowing due to the inertia immediately after operation of the water pump 1 stops, the stress concentration is hard to occur at the fitting part 20.

As described above, since the fitting part 20 is shaped into a shape that avoids the stress concentration, it is possible to effectively suppress deformation or breakage of the drive shaft 7 (the fitting part 20).

Additionally, in the present embodiment, the drive shaft 7 contains the glass fiber 26, and this glass fiber 26 has the effect of increasing rigidity of the drive shaft 7 against force in a direction orthogonal to an oriented direction. That is, since the glass fiber 26 b existing close to the outer peripheral surface of the drive shaft 7 is oriented along the axial direction, rigidity (torsional rigidity) of the drive shaft 7 against or with respect to the rotation direction that is an orthogonal direction is increased.

Especially in the present embodiment, all the outer peripheral surfaces of the fitting part 20 are formed by a curved surface, and its surface area is larger than a shape having a linear part. Thus, since a rate of the glass fiber 26 b that is oriented in the direction orthogonal to the rotation direction is increased, the torsional rigidity of the fitting part 20 (or of the drive shaft 7) is further increased.

Consequently, it is possible to further effectively suppress deformation or breakage of the drive shaft 7 (the fitting part 20).

Further, in the present embodiment, since the fixing of the impeller 8 to the drive shaft 7 is carried out from the axial direction, fixing workability can be improved. In addition, since strong load is not applied to the tip end of the drive shaft 7 from the radial direction, the fixing operation can be carried out without deforming the drive shaft 7.

Furthermore, since the drive shaft 7 and the impeller 8 can be disconnected only by removing the push-nut 25, workability of disassembly is also improved as compared with a connecting or bonding manner such as press-fit and welding.

Second and Third Embodiments

FIGS. 9A and 9B show a second embodiment. Although a basic structure is the same as that of the first embodiment, a different point is that the fitting part 20 of the middle diameter shaft portion 7 b of the drive shaft 7 and the large diameter fitting hole portion 23 a of the impeller 8 are formed into a substantially oval shape in cross section.

FIGS. 10A and 10B show a third embodiment. Although a basic structure is the same as that of the first embodiment, a different point is that the fitting part 20 of the middle diameter shaft portion 7 b of the drive shaft 7 and the large diameter fitting hole portion 23 a of the impeller 8 are formed into a substantially ellipse shape in cross section.

In the same manner as the first embodiment, since shapes of outer peripheral surfaces of these fitting parts 20 are a shape having no corner or no edge, it is possible to lessen a local stress concentration occurring inside the fitting part 20.

Fourth and Fifth Embodiments

FIGS. 11A and 11B and FIGS. 12A and 12B show fourth and fifth embodiments. In the both embodiments, the fitting part 20 of the middle diameter shaft portion 7 b of the drive shaft 7 and the large diameter fitting hole portion 23 a of the impeller 8 are formed into a polygonal shape in cross section.

In the fourth embodiment shown in FIGS. 11A and 11B, the fitting part 20 and the large diameter fitting hole portion 23 a are formed into a substantially hexagonal shape in cross section.

In the fifth embodiment shown in FIGS. 12A and 12B, the fitting part 20 and the large diameter fitting hole portion 23 a are formed into a substantially quadrangle shape in cross section.

Although outer peripheral surfaces of these fitting parts 20 have a plurality of corners 27 (edges) and the stress concentration is apt to occur in a position close to the corner 27 as compared with the first embodiment etc., since the corners 27 firmly bite or are engaged with the inner circumferential surface of the large diameter fitting hole portion 23 a, it is possible to further suppress the idle or racing of the drive shaft 7 with respect to the impeller 8 (see FIG. 11B and FIG. 12B). Here, in order to avoid an excessive stress concentration, each of the corners 27 is rounded.

The present invention is not limited to the above embodiments, and includes all design modifications and equivalents belonging to the technical scope of the present invention.

For instance, in each embodiment, the drive shaft 7 and the pulley 5 are integrally molded. However, these drive shaft 7 and pulley 5 could be separate members.

Further, in each embodiment, as the restraining part that restrains or restricts the maximum fitting position of the impeller 8 with respect to the drive shaft 7, the first and second stepped portions 22 and 24 are used. However, the restraining part is not limited to the stepped portions.

Furthermore, in each embodiment, as the fixing member, the push-nut 25 is used. However, the fixing member is not limited to the push-nut 25. For instance, a snap ring could be used as the fixing member. 

1. A water pump comprising: a drive shaft inserted and located in an inside of a pump housing and formed with synthetic resin material; a pulley provided at one end portion of the drive shaft and rotating integrally with the drive shaft, the pulley being configured to rotate by transmission of power from a drive source; and an impeller formed with synthetic resin material, having a fitting hole and fitted onto the other end portion of the drive shaft through the fitting hole, and wherein the drive shaft and the impeller are configured so that a restraining part that restrains a maximum fitting position of the impeller in an axial direction is provided between the other end portion of the drive shaft and the fitting hole of the impeller, a fixing member that restrains an axial direction movement of the impeller positioned in the maximum fitting position in cooperation with the restraining part is provided at a tip end side of the other end portion of the drive shaft, and a cross-sectional shape of a fitting part, which is fitted into the fitting hole of the impeller, of the other end portion of the drive shaft is formed as a rotation restraining part, and a cross-sectional shape of the fitting hole of the impeller is formed into the same cross-sectional shape as the fitting part of the other end portion of the drive shaft, as the rotation restraining part.
 2. The water pump as claimed in claim 1, wherein: the cross-sectional shape of the fitting part of the other end portion of the drive shaft is formed into a shape having no corner, and the cross-sectional shape of the fitting hole of the impeller is formed into a shape having no corner which is the same shape as the fitting part of the other end portion of the drive shaft.
 3. The water pump as claimed in claim 2, wherein: the whole cross-sectional shape of the fitting part of the other end portion of the drive shaft is formed into a curved surface shape, and the whole cross-sectional shape of the fitting hole of the impeller is formed into a curved surface shape which is the same shape as the fitting part of the other end portion of the drive shaft.
 4. The water pump as claimed in claim 3, wherein: the cross-sectional shape of the fitting part of the other end portion of the drive shaft is formed into a smooth recessed and bulging shape, and the cross-sectional shape of the fitting hole of the impeller is formed into a smooth recessed and bulging shape which is the same shape as the fitting part of the other end portion of the drive shaft.
 5. The water pump as claimed in claim 4, wherein: the synthetic resin material forming the drive shaft contains glass fiber, and the glass fiber existing close to an outer peripheral surface of the drive shaft is oriented along an axial direction of the drive shaft.
 6. The water pump as claimed in claim 5, wherein: the cross-sectional shape of the fitting part of the other end portion of the drive shaft is formed into a shape whose cross section is symmetrical about a shaft center of the drive shaft, and the cross-sectional shape of the fitting hole of the impeller is formed into a shape whose cross section is symmetrical about a center of the impeller.
 7. The water pump as claimed in claim 3, wherein: the cross-sectional shape of the fitting part of the other end portion of the drive shaft is formed into an oval shape, and the cross-sectional shape of the fitting hole of the impeller is formed into an oval shape which is the same shape as the fitting part of the other end portion of the drive shaft.
 8. The water pump as claimed in claim 1, wherein: the cross-sectional shape of the fitting part of the other end portion of the drive shaft is formed into a polygonal shape, and the cross-sectional shape of the fitting hole of the impeller is formed into a polygonal shape which is the same shape as the fitting part of the other end portion of the drive shaft.
 9. The water pump as claimed in claim 8, wherein: the polygonal shape is a hexagonal shape.
 10. The water pump as claimed in claim 8, wherein: the polygonal shape is a quadrangle shape.
 11. The water pump as claimed in claim 1, wherein: the other end portion of the drive shaft protrudes from the fixing member.
 12. The water pump as claimed in claim 11, wherein: the fixing member is fixed to the outer peripheral surface of the drive shaft by point-contact or line-contact.
 13. The water pump as claimed in claim 12, wherein: the fixing member is a snap ring.
 14. The water pump as claimed in claim 13, wherein: the snap ring is a push-nut.
 15. The water pump as claimed in claim 1, wherein: the drive shaft is formed into a tapered shape whose diameter becomes larger toward the pulley.
 16. A water pump comprising: a pump housing having, one end side in an axial direction thereof, a cylindrical portion; a drive shaft rotatably supported in the pump housing and formed with synthetic resin material; a pulley formed with synthetic resin material and having: a disk-shaped end wall integrally fixed to one end portion of the drive shaft; and a cylindrical base portion integrally connected to an outer peripheral edge of the end wall and encircling the cylindrical portion of the pump housing; a cylindrical metal member fixed to an inner circumferential side of the cylindrical base portion of the pulley; a bearing unit interposed between the metal member and the cylindrical portion of the pump housing and rotatably supporting the drive shaft; and an impeller formed with synthetic resin material and fitted onto the other end portion of the drive shaft through a fitting hole provided at the impeller, and wherein the drive shaft and the impeller are configured so that a restraining part that restrains a maximum fitting position of the impeller in an axial direction is provided between the other end portion of the drive shaft and the fitting hole of the impeller, a fixing member that restrains an axial direction movement of the impeller positioned in the maximum fitting position in cooperation with the restraining part is provided at a tip end side of the other end portion of the drive shaft, and a cross-sectional shape of a fitting part, which is fitted into the fitting hole of the impeller, of the other end portion of the drive shaft is formed as a rotation restraining part, and a cross-sectional shape of the fitting hole of the impeller is formed into the same cross-sectional shape as the fitting part of the other end portion of the drive shaft, as the rotation restraining part.
 17. A method for assembling a water pump, the water pump having a drive shaft inserted and located in an inside of a pump housing and formed with synthetic resin material; a pulley provided at one end portion of the drive shaft, rotating integrally with the drive shaft and configured to rotate by transmission of power from a drive source; an impeller formed with synthetic resin material and fitted onto the other end portion of the drive shaft; and a hollow fixing member fixed to the other end side of the drive shaft with respect to the impeller, the method comprising: fitting the impeller onto the other end portion of the drive shaft from a tip end of the other end portion of the drive shaft in an axial direction of the drive shaft and pushing the impeller up to a position in which a movement of the impeller toward the pulley is restrained by a restraining part provided between the impeller and the drive shaft; and fitting the fixing member onto the other end portion of the drive shaft from the tip end, which protrudes from the impeller, of the other end portion of the drive shaft in the axial direction and fixing the fixing member to the other end portion of the drive shaft at a front end surface position of the impeller.
 18. The method for assembling the water pump as claimed in claim 17, wherein: the fixing member is fitted onto the other end portion of the drive shaft from the tip end of the other end portion of the drive shaft in the axial direction and engaged with the other end portion of the drive shaft.
 19. The method for assembling the water pump as claimed in claim 18, wherein: the fixing member is engaged with and fixed to the other end portion of the drive shaft by bite of a nail portion formed on an inner circumferential side of the fixing member into the other end portion of the drive shaft. 